Heat developable photographic light-sensitive materials and the image formation process thereof are well known in the art and are described, e.g., in Shashin Kogaku no Kiso (Foundamentals of Photographic Engineering), pages 553-555, Corona (1979), Shashin Joho (Information of Reflection Images), page 40 (April, 1978), Neblett's Handbook of Photography and Reprography, 7th Ed., pages 32-33, Van Nostrand Reinhold Company, etc.
Organic silver salts used in heat developable light-sensitive materials typically include silver salts of aliphatic carboxylic acids or aromatic carboxylic acids. Silver salts of aliphatic carboxylic acids having a thioether group as disclosed in U.S. Pat. No. 3,330,663 are also employed.
However, these conventional carboxylic acid silver salts have a disadvantage in that reaction between these silver salts and a reducing agent results in release of an acid, which reduces the pH of a layer. As a result, the subsequent development may be inhibited.
Organic silver salts, other than the carboxylic acid salts described above, have been employed and include silver salts of compounds having a mercapto group or thione group or derivatives thereof. In addition, Japanese Patent Publication Nos. 30270/69 and 18416/70 disclose silver salts of compounds having an imino group, such as benzotriazole and its derivatives.
These silver salts, however, involve a disadvantage in that reaction with a reducing agent results in a release of a compound that causes development inhibition and, in some cases, fogging. Further, some of these compounds inhibit the activity of spectral sensitizing dyes. This results in failure to obtain high sensitivity.
In order to eliminate these disadvantages, heat decomposable organic silver salts have been proposed in Japanese Patent Application (OPI) No. 211454/85 (the term "OPI" as used herein refers to a "published unexamined Japanese patent application") (corresponding to European Pat. No. 143,424 A2). Although these compounds are excellent in providing images of high density in a short time, they are still unsatisfactory in terms of stability during preservation and need further improvement.
Heat developable light-sensitive materials frequently contain a base or a base precursor for heat development acceleration. In particular, a base precursor capable of releasing a basic material upon heat decomposition has been employed to advantage in view of preservability. In this case, as the content of the base precursor in the light-sensitive material increases, development is accelerated but, in turn, unfavorable side effects, such as increase in fog, inhibition on sensitizing dyes, and the like, are accompanied. Therefore, it is desirable to use such a base precursor in a low concentration as possible.
As a result of the above, it has been desired to develop a highly active organic silver salt that can provide images of high density with a small amount of a base precursor.